Core DefaultContent Importer does not set isSyncing

Problem/Motivation

The DefaultContent Importer has been copied from said module into core.
It does not set isSyncing on import.
See DefaultContent issue 🐛 DefaultContent Importer does not set isSyncing Needs review and fix there.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet